Oil shale is an abundant energy source rich in hydrocarbons. Many countries, including the United States, China, Brazil, and Estonia, rely on it as a significant energy resource despite the challenges involved in its extraction.

In a recent study published in Energy Reviews, lead author Kun Zhao of China University of Petroleum and others explore the use of terahertz (THz) spectroscopy as a tool in optimizing the utilization of oil shale resources.

In their study titled “Characterization and evaluation of oil shale based on terahertz spectroscopy: A review”, the researchers found that THz technology could be utilized for real-time monitoring of deep underground cracking processes and the productivity of oil and gas.

What is oil shale?

Oil shale is a fine-grained sedimentary rock that is rich in kerogen, which can be converted into oil and gas through pyrolysis processes.

The complexity of the organic matter and minerals within oil shale contributes to the challenges in understanding its oil generation potential and the dynamics of organic matter pyrolysis.

Traditional methods for oil shale evaluation

A variety of traditional methods have been employed for the evaluation of oil shale, including thermogravimetry analysis (TGA), well logging, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and mass spectroscopy.

These methods, according to researchers’ analysis, often involve sample destruction or significant alteration, which limits their effectiveness in providing in-situ information about the material existing in the oil shale.

Additionally, techniques like scanning electron microscopy (SEM) and computed tomography (CT) are used for microscopic characterization, but they also face challenges in accurately separating kerogen from the surrounding mineral, which complicates the analysis of its geophysical characteristics. Further advancements in these techniques are necessary to enhance the understanding and evaluation of oil shale resources.

THz Spectroscopy technology

The researchers reviewed the sensitivity of THz waves to various components of oil shale, including clay minerals, organic matter, and microcracks, which significantly affect the material’s anisotropy.

They revealed that THz waves are sensitive to the polar compounds present in kerogen, enabling the direct assessment of oil content without the need for pyrolysis.

Even when the pyrolysis process is applied, THz spectroscopy can monitor the entire procedure in real-time. This includes the detection of oil and gas volatilization as well as mineral decomposition, providing valuable insights into the efficiency of the pyrolysis process.

THz technology can also characterize the anisotropic properties of oil shale, which are influenced by the arrangement of organic matter and minerals.

Thus, technology helps identify areas rich in kerogen versus those that are poor in kerogen.

The researchers noted the recent advancements in THz near-field microscopy have achieved nanoscale resolution, which could benefit the characterization of unconventional oil and gas reservoirs.

Looking ahead, THz technology could be applied for downhole in-situ mining of oil shale. This method involves direct thermal cracking of oil shale underground, which could lead to more efficient extraction processes.